The invention relates generally to the manufacture of semiconductor devices. More particularly, the invention relates to a chemical dispensing system for semiconductor wafer processes such as removing the edge bead formed during spin coating processes.
Coating materials such as photoresist are typically applied to a semiconductor wafer by flowing liquid coating material onto the top surface of the wafer while it is spinning. The wafer is held on a disk shaped, rotating spin chuck. The diameter of the chuck is slightly less than the diameter of the wafer. The chuck is positioned so that the wafer lies on the chuck in a level horizontal plane. In operation, the backside or inactive surface of the wafer is placed onto the chuck. The chuck applies a suction to the backside of the wafer to hold the wafer in place on the chuck. The chuck is rotated by a motor driven axle that extends down from the chuck. As the wafer is rotated on the chuck, liquid photoresist material is applied to the center of the wafer. The photoresist spreads radially outward from the center of the wafer towards the edge to coat the top of the wafer. Ideally, all excess coating material is ejected from the edge of the wafer. In practice, however, some excess photoresist tends to collect at and form a bead along the edge of the wafer.
A solvent is dispensed along the edge of the wafer to dissolve the edge bead and remove the resist from the extreme edge of the wafer. The solvent may be dispensed through a nozzle directed toward the backside edge of the wafer, in which case it curls up around to the top of the wafer to dissolve the edge bead, or the solvent may be dispensed directly onto the top edge of the wafer. In either case, the process allows solvent and dissolved photoresist to be splashed about and often leaves a jagged edge profile on the photoresist or other coating material.
Accordingly, it is one object of the invention generally to increase the effectiveness of conventional edge bead removal systems. It is another object to control solvent and particle splashing during the process of removing the edge bead from the coating material. It is a further object of the invention to improve the edge profile of the coating material. These and other objects and advantages may be achieved in general by a method for dispensing a chemical, such as an edge bead removal solvent, onto a semiconductor wafer. The method comprises the steps of dispensing the chemical selectively onto the wafer and applying a suction to the area immediately surrounding the location at which the chemical is dispensed onto the wafer. Preferably, the suction is applied substantially simultaneously with the dispensing of the chemical.
One specific version of the invention provides an edge bead removal system wherein suction is applied to the area immediately surrounding the solvent dispensing nozzle to remove dissolved coating material and excess solvent from the wafer. In one aspect of this system, an apparatus for removing the edge bead includes a mechanism for dispensing a solvent selectively onto the edge of the wafer, and a mechanism surrounding the dispensing mechanism for vacuuming excess solvent and dissolved coating material from the edge of the wafer. The edge bead removal apparatus preferably also includes mechanisms for spinning the semiconductor wafer and coating material on the spinning wafer. Another aspect of the system provides a method for removing an edge bead of a coating of material that has been spun onto the surface of a semiconductor wafer. The method includes the steps of dispensing a solvent selectively onto the edge of the wafer to dissolve the coating material at the extreme edge of the wafer, and applying a suction to vacuum excess solvent and dissolved coating material from the wafer. Preferably, the suction is applied to the area immediately surrounding the location at which the solvent is dispensed onto the wafer simultaneously with the dispensing of the solvent.